Last week, as shadow writing to my review of Grudem's Systematic Theology, I at least started my own biblical theology.
1 Introduction to Biblical Theology
For at least this week, I continue with this post on revelation.
From Text to Scripture
What did the biblical texts think they were? This question, at least initially, is a question of genre. It is also a question whose answer no doubt changed over time. When Paul wrote his letters, he surely thought he was writing letters, not Scripture. It is also true that he believed himself to have authority to make commands on behalf of God to at least some of his audiences.
Perhaps the most interesting exchange along these lines is when he processes divorce with the Corinthians. He makes a distinction presumably between what the Lord Jesus said while he was on earth and Paul's own sense of things.  In the one case, Paul was relaying what "not I but the Lord" said (1 Cor. 7:10, NRSV). In the other, he relayed what "I and not the Lord" said (7:12). But he concludes the chapter with his sense that "I think I too have the Spirit of God" (7:40).
Paul considered himself an apostle (e.g., 1 Cor. 9:1). He believed he had more authority than your average Christ-follower. But there is no evidence in any of his writings that he saw the gift of prophetic speech--bringing God's will to bear on a contemporary situation--as something restricted to the first century. His words are something a pastor today might say when presenting what she thinks is God's will: "I think I too have the Spirit of God."
It is thus after the fact that Paul's authoritative letters to specific churches became recognized as Scripture.  The prophets of the Old Testament spoke to Israel with a similar authority, although probably presented with even more confidence. They strongly believed that they were bringing God's voice directly to bear on their immediate situations. Their individual oracles were then later collected and perhaps in some cases extended to give words to Israel that reached beyond their lifetimes.
If one accepts the prevailing theories of sources behind the Pentateuch and historical books, their materials began in part as various stories within Israel--for example, an epic in the southern kingdom of Israel's prehistory. Some of these individual stories were etiologies, explanations of why Israel did or didn't do various things (e.g., why they didn't eat the sinew of the hip, Gen. 32:32). Nothing keeps us from believing by faith that the core legislation of the Pentateuch goes back to Moses at the time of the exodus from Egypt. 
In the prevailing theories, these sources were edited together into their current form in the period after the exile. It seems quite possible to believe that the Pentateuch was mostly if not completely in its current form when Ezra went to Israel from Persia under King Artaxerxes (Ezra 7:14). From that point on it took on the status of law, while before its contents seem largely to have been ignored (e.g., 2 Kings 22:13).
The historical books, the so called "deuteronomistic history," may have reached a form something like its current one by the end of the exile. Although many, many psalms reach back into the time of the first temple, the book of Psalms was almost certainly assembled into a form more like we know it during the second temple period as part of temple worship. They served then a function similar to what they do now as catalysts of our praise and thanksgiving, as well as vehicles for us to bring our sorrows and pains to God.
By the late second century BC, the preface to the book of Sirach testifies to the three-fold form of what we call the Old Testament: the Law, the Prophets, and the other writings. Luke 24:44 similarly divides the Scriptures into the Law, the Prophets, and the Psalms. The contents of the final section may still have been a little fuzzy, but the idea of "the Scriptures" was clearly in place at the time of Jesus.
What did the New Testament authors now understand these Scriptures to be...
 I say "presumably" because some think Paul may be referring to a word from the risen Lord rather than Jesus while on earth. However, given that we have Jesus tradition about divorce in the gospels, this approach seems less likely to me.
 2 Peter 3:16 seems to indicate that by the time of 2 Peter, Paul's letters had already reached the status of Scripture. There is disagreement over the dating of 2 Peter, with most scholars thinking it is a sort of "testament" written to bring Peter's voice to the late first century or early second century church. However, most evangelical scholars do not accept the possibility of pseudonymous writings in the New Testament at all, since they find it difficult not to conclude that lying would inevitably be involved. Those evangelical scholars that accept the possibility do not think deception had to be involved but that it is simply a question of genre, such as in the case of a parable.
 I say "by faith" because archaeology has left us with no ancient trace of Moses from his own time. We only have the Pentateuch itself, which has led certain "minimalists" to deny he ever existed.